FIELD OF THE INVENTION:
This invention relates to an automated method for welding of two pipes for high
temperature and high pressure applications in boilers and heat exchangers.
BACKGROUND OF THE INVENTION:
In Power Boilers large diameter pipes are widely used for carrying medium such
as steam and water at high temperature and high pressure and are commonly
known as pressure parts of a boiler / heat exchanger. The pipe weld joints
should meet the stringent weld quality requirements of American Society for
Mechanical Engineers code ASME Sec I and or such other International
standards. As per these standards, in pipe built welds defects like lack of fusion,
crack, slag inclusion, porosity, etc. are not acceptable. These defects could be
detected by Radiographic or Ultrasonic Non Destructive testing method.
Hitherto, the pipes are being welded with manual Gas Tungsten Arc Welding
(GTAW) also known as Tungsten Inert Gas Welding (TIG) for root pass to ensure
uniform penetration to ensure leak proof joints. Subsequent passes are welded
by shielded Metal Arc Welding (SMAW) also known as Manual Metal Arc Welding
(MMAW). This manual processes leads to increased arcing time, heat input and
resulting in poor efficiency of resources. This also leads to increased cycle time
and affects the productivity. In a typical 500 MW boiler, at least 500 pipe joints
are to be welded at the construction site, besides the large number of joints
made at shops.
To ensure higher productivity with reduced rework and assured quality, a new
automated method of welding the high temperature and high pressure pipes has

been developed. This invention is related to automated process for pipe welding
with GMAW process and process parameters.
An United States Patent 4,088,865: Peters, et al. May 9, 1978
discloses a teaching of
"Laser beam welding apparatus": Welding apparatus featuring a right angle
beam handling tube for directing a fixed laser beam from an entrance to the
tube to a rotatably supported output reflector in a focus head mounted on an
outlet of the tube. The tube has upstream and downstream duct sections which
are independently extendible and retractable relative to their juncture, the
juncture and a laser beam translating mirror mounted therein being movable
only in a linear direction coincident with the incoming beam axis along the
upstream duct section to ensure beam alignment with the entrance and outlet of
the right angle beam handling tube while permitting the distances there between
to vary to selectively position the focus head relative to a work piece.
This patent discloses a teaching on laser beam welding technology and
it is not connected with the process of the instant application.
Another United States Patent 4,207,121: Nakabayashi June 10,1980
discloses a teaching of
"High performance fused flux for submerged arc welding": A fused flux
for use especially in submerged arc welding of high strength, low-alloy pipe
steels, characterized in that the flux is amorphous and nonpowdery and capable
of producing low oxygen content weld metal having a high impact strength even
at low temperature, the flux containing: 20-60 wt. % CaO; 15-55 wt. %
SiO.sub.2 ; 5-10 wt. % CaF.sub.2 ; 5-15 wt. % TiO.sub.2 ; 0-5 wt. % Al.sub.2
O.sub.3 ; 3-15 wt. % Na.sub.3 AIF.sub.6 ; and 5-30 wt. % MgO.

This patent is on submerged arc welding technology using a type of
flux which is different from the process of the teaching of the instant
application.
A further United States Patent 4,256,949: Baumann, et al. March 17,
1981 discloses a teaching of
"Method and wire for submerged arc welding of pipe": A combination of
welding wire and welding flux for submerged arc welding of high strength low
alloy pipe which require low temperature impact properties of at least 30 ft/lb.
at -13.degree. F. The wire consists essentially of 2.0 to 3.5 wt. % manganese;
0.01 wt. % to 1.5 wt. % silicon; 0.05 to 0.15 wt. % carbon; balance iron with
the proviso that when manganese is greater than 2.5 up to 3.5 wt. % the silicon
content is between 0.01 wt. % to 1.5 wt. % and when the manganese content is
between 2.0 to 2.5 wt. % the silicon content is greater than 0.3 wt. % up to 1.5
wt. %. The flux used with these wires is preferably acidic in nature.
This patent is on submerged arc welding technology which is different
from the process as disclosed in the instant specification.
An yet further United States Patent 7,241,961: Duret, et al. July 10,
2007 discloses a teaching of
"TIG welding method": A TIG welding method of welding a first part with a
first wall and an end edge to a second part with a second wall and an edge along
a junction surface between said edges and along which the first wall forms a
salient angle with the second wall. The TIG welding electrode is moved along the
junction surface to weld the first part to the second part. The electrode being
aligned on the side of the salient angle at an angle (.beta.) with respect to the
first wall smaller than 180.degree. and with the longitudinal axis of the electrode
running through the re-entrant angle associated with the salient angle.

This patent is on Tungsten Inert gas arc welding technology which is
different from the process of the instant invention.
A still further United States Patent 6,160,241: Stava, et al. December
12, 2000 discloses a teaching of
"Method and apparatus for electric arc welding": An electric arc welding
apparatus for depositing molten metal from an advancing welding wire into a
weld puddle in an open root between two juxta positioned plates where the root
extends in a welding path and is formed by converging walls terminating in
generally parallel walls spaced to define a gap, which apparatus comprises a
contact holder with a wire outlet, a switching power supply directing welding
current to the wire as the wire passes from the outlet toward the open root, with
the advancing wire defining an electrode stick out between the contact holder
and the weld puddle, a circuit for sensing the length of the stick out, and control
means for adjusting the welding current as a function of the sensed stick out
length.
This patent is on general electric arc welding technology which is
different from the orbital process as describes in the present invention.
An yet another United States Patent 5,713,312: Waryasz February 3,
1998 discloses a teaching of
"Syngas cooler with vertical surface super heater": A syngas cooler
apparatus includes an elongated generally cylindrical pressure vessel having an
axial extremity that is a top end during normal operation of the cooler and an
axial extremity that is a bottom end during normal operation of the cooler. A
laterally extending support member extends within the pressure vessel proximate

to the top end and front, back, and two side walls define at least one flow
channel in the pressure vessel. The pressure vessel has an inlet and an outlet
communicating with the flow channel. A pendant heat exchanger surface
comprising a plurality of loops is disposed in the flow channel. Each of the loops
is formed from tubing and the major portion of the entire axial extent of the
tubing are rectilinear axial sections that are disposed with the axes thereof
substantially in a vertical plan during normal operation. The pendant is disposed
in the flow channel intermediate the inlet and the outlet and is supported solely
from the laterally extending support member.
This patent is not related to welding process.
A still another United States Patent 5,396,039: Chevrel, et al. March
7,1995 discloses a teaching of
"Process for assembling piping or components by TIG welding": A
process to avoid or limit corrosion at the junction of two piping comprising
devices welded together, said piping comprising devices being adapted to flow
corrosive gases through them, said process comprising the steps of: a) providing
a first piping comprising device and connecting it to an inert gas source; b)
purging it with an inert gas comprising substantially not more than 10 ppb of an
oxidizing gas selected from the group consisting of oxygen, carbon dioxide,
water vapor or mixtures thereof, said inert gas flowing from a first opening to a
second opening of said piping comprising device; c) providing a second pipe
comprising device in flow communication with the first one, while continuing to
purge the first piping comprising device; d) welding the two piping comprising
devices, said welding being carried out under an inert gas atmosphere; and e)
repeating steps c and d if necessary.
This patent is on Tungsten Inert gas arc welding technology which is
different from the process as mentioned in the instant invention.

Therefore, through the patent search, we could not get a patent similar or
identical one to our claim of invention.
OBJECTS OF THE INVENTION:
It is therefore, an object of the present invention to propose an automated
method for welding two pipes for high temperature and high pressure
applications in boilers and heat exchangers which eliminates the disadvantages
of the Prior Art.
Another object of the present invention is to propose an automated method for
welding of two pipes for high temperature and high pressure applications in
boilers and heat exchangers which increases productivity and quality of weld
joint.
A further object of the present invention is to propose an automated method for
welding of two pipes for high temperature and high pressure applications in
boilers and heat exchangers which upgrades the skill of the operator through
improved process and automation.
An yet further object of the present invention is to propose an automated
method for welding two pipes for high temperature and high pressure
applications in boilers which replaces the low productive TIG/GTAW by modified
short circuit welding process such as SIT/RMD/wise root GMAW process to get
quality weld joints with higher productivity.

A still further object of the present invention is to propose an automated method
for welding of two pipes for high temperature and high pressure applications in
boilers and heat exchangers which stores the parameter in the system and uses
repeatedly to ensure quality.
One more object of the present invention is to propose an automated method for
welding of two pipes meeting the stringent quality requirements of International
codes such as Indian Boiler Regulations (IBR) and American Society for
Mechanical Engineers (ASME) sec. V.
SUMMARY OF THE INVENTION:
A welding automation method for high temperature and high pressure
application comprising at least two pipes (2) to be welded and prior preparation
of a double V compound angle groove at face to face junction of two pipes (2)
and clamping circular ring (3) over outer diameter of one side of the pipe (2) to
pipe joint and placement of welding machine (5) with the help of travel wheels
(rollers) (9) over the ring (2) mounted on the pipe to be welded and placement
of welding torch attached with the suitable contact tip (11) on the double V
compound angle groove of junction point of the pipes (2) and power on the
welding machine (5) to start welding on the double V compound angle groove
and start rotation of orbital head by the positive drive of guide roller (9) on one
edge of the ring guided to the pipe and simultaneously starts uncoiling of the
welding wire from the spool; characterized in that once the welding starts, a
medium amperages excites in the closed loop electrical circuit melts continuously
the end of the solid wire with a variable feed rate setting in different segments of
the pipe and on completion of welding, stops rotation of orbital head.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 01 indicates the welding of pipe joint using the method.
Figure 02 shows the contact tip modified and used for this process.
Figure 03 shows the nozzle design to make the welds.
Figure 04 shows the line diagram of two pipes face to face position with a
double V compound angle groove.
Figure 05 shows a line diagram of the front view of automated welding process.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION:
The pipes used in power boilers involve higher wall thickness up to 50 mm and
involves a special joint preparation involving double V compound angle. The
narrow groove joint resulting from higher wall thickness requires a special
nozzle, contact tip and robust welding procedure to achieve defect free welds all
around. To perform such welding a modified contact tip (fig. 2 & 3) was
developed which comprises a small knife shape having one round end (10) for
gripping in the holder and the other end is a sharp contact edge (11) which is
capable of entering in the narrow groove. The Nozzle is provided with through
holes, one central hole (12) for passage of welding wire and one peripheral hole
(13) for gas passage. As shown in fig-4, two such pipes (2) are prepared for
welding. Pipe (2) is mounted over the stand (10b) guided with v block (10a) only
one side of the pipe while other side is over hanged with the help of the tack
weld with other pipe. Pipe will be stationary over the v block (10a) while the
weld head will be rotating over guide ring (3) as shown in fig 1.

As shown in fig-1 & 5 , the pipes (2) are prepared for welding the pipes (2) are
to be welded is placed inside a mounting ring (3) disposed below the orbital
head (5) and rest on a plurality supporting rollers (9). The welding torch with
nozzle (14) and contact tip (11) is attached with the orbital head. The welding
wire stored in a spool (6) disposed at the back side of orbital head (5) and the
wire is passing through the orbital head (5) from the spool (6) and enters in the
contact tip (11) of the nozzle (14). The machine is operable through a power
source (1).
Here pipe is fixed and orbital head rotates around the pipe in half circles to
complete full welding. The welding starts as soon as the welding wire from
contact tip (11) touches the pipes (2) and once the welding starts a medium
amperages excites in the closed loop electrical circuit melts continuously the end
of the solid wire with a variable feed rate setting in different segments of the
pipe and on completion of welding, stops rotation of the orbital head. So the
welding torches along with orbital head rotate as well as metal deposition takes
place during downhill welding technique. When the welding stopped, the
electrical circuit inside the orbital head defunct and stop the working of guide
roller which in turn stop rotation of welding torch. Gas shielding at fixed flow rate
is provided continuously till the completion of full welding. This system also uses
STT/RMD/wise root GMAW for root pass welding and GMAW for filler passes.

WE CLAIM:
An automated pipe welding method for high temperature and high pressure
application comprising:-
- at least two pipes (2) to be welded;
- prior preparation of a V groove at face to face junction of two pipes (2);
- placement of each pipe (2) inside a mounting ring (3);
- placement of mounting ring (3) beneath the welding machine (5) and rest
on rollers (9);
- placement of travel wheels of orbital head (5) on the mounting ring (2)
attached;
- placement of welding torch attached with a knife shape contact tip (11)
on the V groove of junction point of the pipes (2).
- power on the welding machine (5) to start welding on the V groove and
start rotation of welding torch along with orbital head (5) by the roller
guided to the pipe (2) and start uncoiling of the welding wire from the
spool;
characterized in that once the welding starts, a medium amperages excites in the
closed loop electrical circuit melts continuously the end of the solid wire with a
variable feed rate setting in different segments of the pipe and on completion of
welding, stops rotation of orbital head.
2. The automated welding process as claimed in claim 1 wherein the welding
machine comprising:-

- an orbital head (5) attached with a welding torch and four wheels
operable with electrical power;
- a welding torch attached with nozzle (14) and a knife shaped contact tip
(11);
- a spool for storage of welding wire attached at the back side of orbital
head;
3. The welding machine as claimed in claim 2 wherein the nozzle is provided a
central hole for welding wire passage and a peripheral hole for gas passage.
4. The welding machine as claimed in claim 2 wherein the contact tip is a small
knife shaped having one end with cylindrical head for gripping in the
machine and other end has a sharp edge for welding.

An automated welding method for high temperature and high pressure
application comprising at least two pipes (2) to be welded and prior preparation
of a double V compound angle groove at face to face junction of two pipes (2)
and clamping circular ring (3) over outer diameter of one side of the pipe to pipe
joint and placement of welding machine (5) with the help of travel wheels (8)
over the ring (2) mounted on the pipe to be welded and placement of welding
torch attached with a knife shape contact tip (11) on the double V compound
angle groove of junction point of the pipes (2) and power on the welding
machine (5) to start welding on the double V compound angle groove and start
rotation of orbital head (5) by the positive drive of guide roller on one edge of
the ring guided to the pipe (2) and simultaneously starts uncoiling of the welding
wire from the spool; characterized in that once the welding starts, a medium
amperages excites in the closed loop electrical circuit melts continuously the end
of the solid wire with a variable feed rate setting in different segments of the
pipe and on completion of welding, stops rotation of orbital head.